The research described in this application is designed to test the hypothesis that long term arterial dilator therapy alters the natural history of aortic insufficiency. The proposed study is a double blind, placebo controlled clinical trial evaluating the effects of hydralazine therapy in patients with chronic severe aortic insufficiency. Initial and follow-up evaluation of patients will utilize non-invasive methods (eg, treadmill testing, echocardiography, radionuclear angiography) exclusively. The trial is planned to extend for 3 years with patient recruitment expected to be completed by the end of the first year. The major question to be addressed is whether the long term administration of oral hydralazine (in an attempt to lower systemic vascular resistance and thereby decrease the amount of regurgitation and volume overload) will alter the progression of left ventricular dilation or even lead to regression in heart size. An intimately related question of considerable clinical importance is whether the progression of left ventricular dysfunction often manifest by patients with aortic insufficiency can be prevented or even reversed. The answers to these questions will shed light on a still more crucial issue - whether the time for aortic valve replacement can be delayed by the long term administration of arterial dilators.